Department of Pathobiological Sciences, Louisiana State University (LSU)-School of Veterinary Medicine, Skip Bertman Dr., Baton Rouge, LA 70803, USA.
Vaccine. 2011 Jan 10;29(3):593-8. doi: 10.1016/j.vaccine.2010.06.040. Epub 2010 Jun 25.
Francisella asiatica is a Gram-negative, facultative intracellular bacteria that causes fish francisellosis. Fish francisellosis is a severe sub-acute to chronic granulomatous disease with high mortalities and high infectivity rates in cultured and wild fish. To date, there is no approved vaccine for this widespread emergent disease. The goal of this study was to characterize the efficacy of a defined F. asiatica mutant (ΔiglC) as a live attenuated vaccine against subsequent immersion challenge with the wild-type (WT) organism. In previous work, the ΔiglC was found to be attenuated upon intraperitoneal injection and immersion challenges. In vitro, the ΔiglC exhibited reduced growth in tilapia head-kidney derived macrophages, and was significantly attenuated (p<0.001) as demonstrated by cytopathogenic and apoptosis assays. In this study, the ΔiglC was tested to determine its ability to protect tilapia against challenge with high doses (lethal dose 80) of WT bacteria. Naïve tilapia vaccinated by immersion with a suspension of the ΔiglC and subsequently challenged with WT F. asiatica were protected (90% mean percent survival) from the lethal challenges. F. asiatica-specific antibodies produced in response to immunization with the ΔiglC were subsequently found to protect naïve tilapia against high-dose F. asiatica challenge in passive immunization experiments. Significant protection (p<0.001) was obtained when fish were passively immunized and challenged with 10(4) and 10(5)CFU/fish of WT F. asiatica; but not when challenged with 10(6)CFU/fish. This is the first report of a defined live attenuated strain providing protection against F. asiatica in fish.
亚洲羊布鲁氏菌是一种革兰氏阴性、兼性细胞内细菌，可引起鱼类弗朗西斯菌病。鱼类弗朗西斯菌病是一种严重的亚急性至慢性肉芽肿性疾病，在养殖和野生鱼类中的死亡率和感染率都很高。迄今为止，这种广泛流行的突发疾病还没有批准的疫苗。本研究的目的是描述一种明确的亚洲羊布鲁氏菌突变体（ΔiglC）作为活减毒疫苗对随后用野生型（WT）生物体进行浸浴挑战的功效。在之前的工作中，发现 ΔiglC 在腹腔内注射和浸浴挑战时会减弱毒力。在体外，ΔiglC 在罗非鱼头肾来源的巨噬细胞中表现出生长减少，并且细胞病变和凋亡测定表明其显著减弱（p<0.001）。在这项研究中，测试了 ΔiglC 抵抗高剂量（致死剂量 80）WT 细菌挑战的能力。用 ΔiglC 悬浮液进行浸浴免疫的幼稚罗非鱼随后用 WT F. asiatica 进行挑战，可免受致命挑战的影响（90%平均存活率）。随后发现，针对 ΔiglC 免疫产生的 F. asiatica 特异性抗体在被动免疫实验中可保护幼稚罗非鱼免受高剂量 F. asiatica 挑战的影响。当鱼用 10(4)和 10(5)CFU/鱼的 WT F. asiatica 进行被动免疫和挑战时，可获得显著的保护（p<0.001）；但当用 10(6)CFU/鱼的 WT F. asiatica 进行挑战时，没有获得保护。这是第一个报告明确的活减毒菌株可在鱼类中提供针对 F. asiatica 的保护的报告。
